Hi guys I've recently re-barrelled my 300 win mag in a 1:12 twist 30" and I can't seem to get hornady 180 sst's or nosler 180 ballistic tips to shoot even close to Moa. I was starting to worry that my new barrel was no good till I shot through some 125gr nosler ballistic tips which shot under 1/2 Moa consistantly. Now I like the 180's for long range hunting but I'm thinking that 180's aren't stabilising?? The guy who sold me the barrel said 180s would be fine but maybe not??? Thought some of you guys might have a good idea.
I am loading with reloader22 1gr under max.

Do you think it would be worth buying a slower burning powder or just give up with the 180s?

Competitive long range shooters using the .300 Win. Mag. have been using 1:12 twists for 180, 190, and 200 grain match bullets for decades. Same for other cartridges pushing these bullets out at 2900 to 3000 fps. Even 1:12 twists in .308 Win. barrels will shoot 180 and 190 grain bullets with match winning accuracy and they aren't spinning as fast as your .300 spins them. Therefore, your bullets are spun fast enough to stabilize them.

If your 1:12 twist barrel won't shoot bullets of that weight accurate, the problem's not the twist. Something else is not right. Powders close to IMR4350 have worked well with 180 to 200 grain bullets in such magnums. Slower ones may shoot 'em out faster, but typically with less accuracy.

What's the make of your barrel and do you know it's bore and groove diameters? If they're larger than the bullets used, then accuracy will not be all that great. Dimensions need be measured to the nearest .0001". Bullets should typically be at least .0003" larger than groove diameter for best accuracy.

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One MOA is a bit better than what was the old standard for "a good hunting rifle" back fifty years ago when even two MOA was acceptable. Most deer--and, likely, elk--are killed inside of 200 yards. Hard to miss a body shot with a one-MOA rifle.

150s would likely group nicely, and that's as much as is ever needed for deer--in some eighty years of my family's experience.

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Have you tried working up the load again and this is the best you can do? Or is this the load that used to work in the old barrel? May just need to back your powder charge down.

I base this on my limited experience with my .308; 1 in 12 on a 20" barrel. 168, 175, 190gr, all can shoot sub-moa but it was never anywhere near the max recommended load; best accuracy was always obtained with charge weights towards the middle to bottom end of the scale.

In response to your question it is a no7 maddco barrel made in Australia. Its a huge barrel and makes the 300 kick like a 308. They're known for producing match grade barrels. Not sure what the bore and groove diameter is though. I will try playing around with the load some more as I was loading them the same as my previous barrel which was 1:11.

If you already tried lighter charges of powder and that did not work, try different bullets. Then different powder. Some barrels just don't like some bullets. I would try some that are not plastic tipped.

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You can't fix stupid....however ignorance can be cured through education!

I am not an expert on this topic, but .300 Win. Mag. hunting rifles, including my Browning A-Bolt SS, have a 1:10 twist rate which, as I understand it, is appropriate (necessary?) to stabilize long 180 to 200 gr. (or heavier) hunting bullets. I am curious about the use of 1:12 twist in a .300 Win. Mag.

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lefteye I am not an expert on this topic, but .300 Win. Mag. hunting rifles, including my Browning A-Bolt SS, have a 1:10 twist rate which, as I understand it, is appropriate (necessary?) to stabilize long 180 to 200 gr. (or heavier) hunting bullets. I am curious about the use of 1:12 twist in a .300 Win. Mag.

I chose a 1:12 because I usually load for speed when im pig hunting as I find it a fair bit easier to place shots on the running target. The game in Australia isn't that big so max I use is 180gr for long range shots on still targets like deer or dingos. Not sure if that reasoning is correct or not because I'm certainly not a professional.

On a good note I tried some different powder as suggested and worked up some loads and I've got marvellous results... Powder I'm using is AR 2217 made by ADI. Not sure the American equivalent. Was blown away by how much the powder changed the accuracy. I got it shooting the best with .5 under max load at about 1/2 MOA using hornady 180gr sst. Even got a nice clean shot at 500yards this afternoon on some dog food

As usual you guys solve my problems so thank you all for the suggestions

Bullet stabilization's all about how many rpm's the bullet spins at for a given muzzle velocity.

Winchester loads 180's in .308 Win. ammo leaving at 2600 fps in their rifle's 1:12 twist barrels. They're well stabilized. So were the Western Cartridge Company's 197 and 200 grain match bullets made to shoot over 100 fps slower from Win. 70 match rifles chambered for the .308 Win. and 1:12 twist barrels.

So were the 180 grain Sierra HPMK's from the Army's M14NM's in competition leaving a bit faster in their 1:12 twist barrels. And they won their share of matches and set a few records with that load. They too, were well stabilized. And the 190 Sierra HPMK's the USN and USAF teams shot from their 7.62 NATO M1's leaving about 2600 fps from their 1:12 twist barrels were another winning combination.

Figure out how fast they spin (rpm's = muzzle fps x 720 / twist in inches). Then compare the rpm's they leave at to what a .300 Win. Mag gets as it pushes 'em out at 3100 fps. in a 1:12 twist barrel. Note that for every 100 fps over about 2500 fps, these bullets need to be spun about 2000 rpm faster to stabilize them due to increased air resistance.

I've shot 180 Sierra HPMK's from a 9-pound 26" barreled .300 Win. Mag. with a 1:12.7" twist; great accuracy all the way to 1000 yards. They left about 3100 fps.

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Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master

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